This invention relates to supply devices for internal combustion engines of the kind which inject fuel into the engine inlet manifold.
Prior art fuel supply devices of the kind set forth comprise a driver-controlled main throttle element located in the intake pipe of the engine and an auxiliary throttle element usually, but not necessarily, disposed upstream of the main throttle element and opening progressively and automatically in proportion as the rate of air flowing through the inlet tube increases. To this end, the auxiliary throttle element can be connected to a movable element subjected to the air pressure prevailing in that portion of the intake pipe which is between the auxiliary throttle element and the main throttle element (at least when the main throttle element is disposed downstream of the auxiliary throttle element). The extent of opening of the auxiliary throttle element is a yardstick for the rate of air flow through the inlet manifold, and a pressure drop which is either substantially constant or which is a predetermined and increasing function of the engine intake air flow is established between the upstream and downstream sides of the auxiliary throttle element.
Such a device is described in French Patent Specification No. 1,519,890.
The fuel injection delivery is controlled by a system having a metering element which is connected to the auxiliary throttle element and which is adapted to move in dependence upon the extent of opening of the latter element so as to vary the fuel flow cross-sectional area proportionally to the air flow cross-sectional area metered by the auxiliary restriction, so that the air fuel mixture remains of substantially constant richness.
That device operates satisfactorily. However the greater part of the pressure drop experienced by the fuel after the fuel pump occurs before the fuel is forced through the injection orifice -- i.e., before the fuel is atomized for introduction into the engine intake manifold. Atomization is of course more complete in proportion as the injection pressure is higher, and if the residual velocity of the fuel in the injection orifice is too low atomization may become inadequate. Pressure losses occurring before injection of the fuel should therefore be kept to a minimum.
The injection device of U.S. Pat. Nos. 2,785,669 and 2,857,203 exhibits the same shortcoming: a notable fraction of the fuel pressure available at the pump outlet is lost in the form of pressure loss before the injection orifice.
It is an object of the invention to provide a fuel supply device which performs better in practice than the prior art, inter alia by greatly reducing the disadvantages mentioned.
According to the invention there is provided a fuel supply device for internal combustion engines having means for injecting fuel under pressure into the engine intake through at least one adjustable cross-sectional orifice of adjustable cross section, an auxiliary throttle element located in the air intake pipe opening automatically and progressively in increasing dependence upon the rate of engine intake air flow, and means for metering the cross-sectional area of the injection orifices as an increasing function of the extent of opening of the auxiliary throttle element and as an increasing function of the difference between the pressures upstream and downstream of the latter element.
The metering means can comprise a piston movable in a stationary tubular member whose side wall is formed with the injection orifice or orifices, the effective cross-sectional area thereof being determined by the position of the piston. The same is secured to a movable element, such as a diaphragm, experiencing the difference between the pressures upstream and downstream of the auxiliary throttle element and to a movable element experiencing a differential pressure which is directly related to the extent of opening of the automatic throttle element.
In the system just defined most of the pressure drop in the fuel circuit occurs at the place where the fuel is injected, and so the flow velocity through the or each injection orifice is used to provide satisfactory atomization.
The invention will be better understood from the following description of an exemplary and non-limitative embodiment, reference being made to the accompanying drawings.